21.1 Introduction
Natural products are the chemicals and compounds that are given to us by nature.
The significance of the nature and the natural products are well understood when we
come to the ecosystem. For the thousands of years, plants are defending and
reigning rank holder which works day and night in their own body for giving us
remarkable natural products. The various and different parts of a plant can be a
good source for natural compounds. Plants metabolize different organic compounds
in their body by complex mechanism comprises physical and chemical episodes of
photosynthesis, respiration, degradation. There are two types of metabolism occurs
in plant system, like primary and secondary metabolism. Primary metabolism yields
primary metabolites which are essential for the growth, development, functioning
and the survival of the plant whereas, secondary metabolites play a direct or indirect
role in plant’s growth and they are not required for a plant to survive. The secondary metabolites of a plant play a key role in plant’s defence system, fighting
herbivores and pathogens. Also they are found useful in other important functions
like giving plant or plant portions a color, maintaining and signaling the primary
metabolic pathways etc. (Mazid et al. 2011). Some of the much known important
secondary metabolites are terpenes, phenolic metabolites, glycosides and alkaloids.
Tannins and polyphenols are one of the most widely used secondary metabolites
obtained from different species of higher altitude plants. It is found from different
parts of myrobalan, nutgall, chestnut, rhubarb, bahera, arjuna, Indian goose berry,
ashoka bark, black and pale catechu, pterocarpus etc. and they are extracted by
maceration. Chemically, they are the mixture of complex organic substances in
which polyphenols are present. Tannins are basically phenylpropanoids, condensed
to lengthy polymers with molecular weight ranging from 300 to 3000 (Khanbabaee
and Van Ree 2001). They are non-nitrogenous and not crystalline in nature, they do
possess a bitter taste and they give positive results with Goldbeater’s skin test
(Nierenstein 1932). Tannins are classified into two types generally, hydrolysable
tannins and condensed tannins. Hydrolysable tannins can be hydrolysed easily by
enzymes or different acids into gallic acid or ellagic acid, which further process
pyrogallol, glucogallin, etc., where condensed tannins do not respond to hydrolysis
and being a flavone derivative, they can be related to flavonoid dyes and pigments or
phlobatannins or proanthocyanidins (Schofield et al. 2001). It is having astringent
property and it helps in precipitation of different proteins, gelatins, glycosides etc.
from any solution. The word ‘tannin’ helps to give a simple knowledge about its
property to tan, i.e. ability to convert leather from skin surface (Sieniawska and Baj
2017). Because of this property, tannins and tannin containing drugs can be used in
burn treatment. Apart from the astringent property, tannins do possess versatile
applications like medicinal uses, industrial uses and biological applications. Tannins
are used to treat different diseases and biological conditions like fever, diarrhea,
diabetes, eye infections, gall bladder stone, intestinal disorder, constipation etc.
(Sieniawska and Baj 2017). Different tannins and tannic acid derivatives obtained
from different parts of plants like roots, barks, stems, leaves, galls, fruits, herbs are
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S. Mal and D. Pal
Natural products are the chemicals and compounds that are given to us by nature.
The significance of the nature and the natural products are well understood when we
come to the ecosystem. For the thousands of years, plants are defending and
reigning rank holder which works day and night in their own body for giving us
remarkable natural products. The various and different parts of a plant can be a
good source for natural compounds. Plants metabolize different organic compounds
in their body by complex mechanism comprises physical and chemical episodes of
photosynthesis, respiration, degradation. There are two types of metabolism occurs
in plant system, like primary and secondary metabolism. Primary metabolism yields
primary metabolites which are essential for the growth, development, functioning
and the survival of the plant whereas, secondary metabolites play a direct or indirect
role in plant’s growth and they are not required for a plant to survive. The secondary metabolites of a plant play a key role in plant’s defence system, fighting
herbivores and pathogens. Also they are found useful in other important functions
like giving plant or plant portions a color, maintaining and signaling the primary
metabolic pathways etc. (Mazid et al. 2011). Some of the much known important
secondary metabolites are terpenes, phenolic metabolites, glycosides and alkaloids.
Tannins and polyphenols are one of the most widely used secondary metabolites
obtained from different species of higher altitude plants. It is found from different
parts of myrobalan, nutgall, chestnut, rhubarb, bahera, arjuna, Indian goose berry,
ashoka bark, black and pale catechu, pterocarpus etc. and they are extracted by
maceration. Chemically, they are the mixture of complex organic substances in
which polyphenols are present. Tannins are basically phenylpropanoids, condensed
to lengthy polymers with molecular weight ranging from 300 to 3000 (Khanbabaee
and Van Ree 2001). They are non-nitrogenous and not crystalline in nature, they do
possess a bitter taste and they give positive results with Goldbeater’s skin test
(Nierenstein 1932). Tannins are classified into two types generally, hydrolysable
tannins and condensed tannins. Hydrolysable tannins can be hydrolysed easily by
enzymes or different acids into gallic acid or ellagic acid, which further process
pyrogallol, glucogallin, etc., where condensed tannins do not respond to hydrolysis
and being a flavone derivative, they can be related to flavonoid dyes and pigments or
phlobatannins or proanthocyanidins (Schofield et al. 2001). It is having astringent
property and it helps in precipitation of different proteins, gelatins, glycosides etc.
from any solution. The word ‘tannin’ helps to give a simple knowledge about its
property to tan, i.e. ability to convert leather from skin surface (Sieniawska and Baj
2017). Because of this property, tannins and tannin containing drugs can be used in
burn treatment. Apart from the astringent property, tannins do possess versatile
applications like medicinal uses, industrial uses and biological applications. Tannins
are used to treat different diseases and biological conditions like fever, diarrhea,
diabetes, eye infections, gall bladder stone, intestinal disorder, constipation etc.
(Sieniawska and Baj 2017). Different tannins and tannic acid derivatives obtained
from different parts of plants like roots, barks, stems, leaves, galls, fruits, herbs are
716
S. Mal and D. Pal